Metal particles from the abrasion of brake pads - up to a fifth of fine particulate matter (PM2.5) air pollution at roadsides - may cause inflammation and reduce the ability of immune cells to kill bacteria a new study has found, similarly to particles derived from diesel exhaust.
The scientists, primarily funded by the Medical Research Council (MRC), part of UK Research and Innovation, say this suggests that particulate pollution from brake wear could be contributing to increased susceptibility to airway infections and other negative effects on respiratory health.
It is estimated that only 7% of PM2.5 pollution from traffic comes from tail pipe exhaust fumes at roadside sites; the rest comes from sources such as tyre, clutch and brake wear, as well as the resuspension of road dust. Brake dust is the source of approximately 20% of total PM2.5 traffic pollution.
These are particles small enough to be inhaled into the deepest regions of the lung - PM2.5 means the particles are less than 2.5 micrometres in diameter.
Much of the research into the effects of traffic air pollution has focused on the effects of particulates derived from the tailpipe of diesel vehicles, but this new study has investigated if the particulate matter in brake dust has similar effects.
Dr Ian Mudway, who led the research at the MRC Centre for Environment and Health at King's College London, said: "At this time the focus on diesel exhaust emissions is completely justified by the scientific literature, but we should not forget, or discount, the importance of other components, such as metals from mechanical abrasion, especially from brakes. There is no such thing as a zero-emission vehicle, and as regulations to reduced exhaust emissions kick in, the contribution from these sources are likely to become more significant."
Image credit: Credit: L. Selley University of Cambridge